WO2013109979A1 - Obturateur optique à commutation rapide permettant de transmettre de façon alternée un rayonnement visible et un rayonnement proche infrarouge - Google Patents

Obturateur optique à commutation rapide permettant de transmettre de façon alternée un rayonnement visible et un rayonnement proche infrarouge Download PDF

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Publication number
WO2013109979A1
WO2013109979A1 PCT/US2013/022287 US2013022287W WO2013109979A1 WO 2013109979 A1 WO2013109979 A1 WO 2013109979A1 US 2013022287 W US2013022287 W US 2013022287W WO 2013109979 A1 WO2013109979 A1 WO 2013109979A1
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Prior art keywords
radiation
liquid crystal
wavelength
wavelength selective
nir
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PCT/US2013/022287
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English (en)
Inventor
Jesper Osterman
Terry J. Scheffer
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Lc-Tec Displays Ab
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Application filed by Lc-Tec Displays Ab filed Critical Lc-Tec Displays Ab
Priority to US14/372,956 priority Critical patent/US9316865B2/en
Publication of WO2013109979A1 publication Critical patent/WO2013109979A1/fr
Priority to US14/334,517 priority patent/US9229139B2/en

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    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
    • G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
    • G02F1/1333—Constructional arrangements; Manufacturing methods
    • G02F1/1335—Structural association of cells with optical devices, e.g. polarisers or reflectors
    • G02F1/13363—Birefringent elements, e.g. for optical compensation
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/0136—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  for the control of polarisation, e.g. state of polarisation [SOP] control, polarisation scrambling, TE-TM mode conversion or separation
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
    • G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
    • G02F1/1333—Constructional arrangements; Manufacturing methods
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
    • G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
    • G02F1/1333—Constructional arrangements; Manufacturing methods
    • G02F1/1335—Structural association of cells with optical devices, e.g. polarisers or reflectors
    • G02F1/133528—Polarisers
    • G02F1/133533—Colour selective polarisers
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
    • G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
    • G02F1/1333—Constructional arrangements; Manufacturing methods
    • G02F1/1335—Structural association of cells with optical devices, e.g. polarisers or reflectors
    • G02F1/13363—Birefringent elements, e.g. for optical compensation
    • G02F1/133636—Birefringent elements, e.g. for optical compensation with twisted orientation, e.g. comprising helically oriented LC-molecules or a plurality of twisted birefringent sublayers
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F2203/00—Function characteristic
    • G02F2203/11—Function characteristic involving infrared radiation
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F2203/00—Function characteristic
    • G02F2203/58—Multi-wavelength, e.g. operation of the device at a plurality of wavelengths

Definitions

  • This application relates to optical shutters and, in particular, to an optical shutter that rapidly switches between optical states to alternately transmit incident visible and near infrared radiation.
  • An optical shutter includes a wavelength selective polarizing filter in optical association with a liquid crystal polarization modulator to rapidly switch between optical states to alternately transmit visible radiation and near infrared radiation.
  • the wavelength selective polarizing filter is constructed to impart a polarization state to incident radiation and transmit polarized radiation within at least the visible
  • the liquid crystal polarization modulator is positioned to receive incident radiation for internal propagation through the liquid crystal polarization modulator and is responsive to a first value and a second value of an applied control signal to switch the internally propagating radiation to, respectively, a first polarization state and a second polarization state.
  • the switching between the first and second polarization states produces, in cooperation with the wavelength selective polarizing filter, optical shutter output radiation in different wavelength regions of the
  • the switching of the internally propagating radiation to the first polarization state causes transmission and blockage of the optical shutter output radiation within, respectively, the visible wavelength region and the near infrared region.
  • the switching of the internally propagating radiation to the second polarization state causes transmission and blockage of the optical shutter output radiation within, respectively, the near infrared wavelength region and the visible wavelength region.
  • the optical shutter has, in optical series
  • a wavelength selective polarizing filter pair that includes a wavelength selective polarizing filter transmitting polarized radiation within the visible wavelength region and a wavelength selective polarizing filter transmitting polarized radiation within the near infrared wavelength region.
  • the wavelength selective polarizing filter that is constructed to impart a polarization state to incident radiation constitutes a broadband wavelength selective polarizing filter that transmits polarized radiation in the visible wavelength region and the near infrared wavelength region.
  • the liquid crystal polarization modulator is positioned between the broadband wavelength selective polarizing filter and the wavelength selective polarizing filter pair.
  • the wavelength selective polarizing filter that is constructed to impart a polarization state to incident radiation constitutes a broadband wavelength selective polarizing filter that transmits polarized radiation in the visible wavelength region and the near infrared wavelength region.
  • the liquid crystal polarization modulator includes a guest-host liquid crystal mixture that includes a liquid crystal director.
  • the guest-host liquid crystal mixture depending on an orientation of the liquid crystal director determined by one of the first and second polarization states to which the internally propagating radiation is switched, exhibits variable absorption of different radiation wavelength regions to produce the optical shutter output radiation in different wavelength regions of the electromagnetic spectrum.
  • the liquid crystal polarization modulator includes a guest-host liquid crystal mixture that includes a liquid crystal director contained between first and second electrodes.
  • the guest-host liquid crystal mixture exhibits variable absorption of different radiation wavelength regions, depending on the orientation of the liquid crystal director relative to the polarization state of the internally propagating radiation.
  • the optical shutter includes first and second wavelength selective polarizing filters imparting a polarization state to incident radiation within the visible wavelength region but not imparting a polarization state to incident radiation within the near infrared wavelength region.
  • the first and second wavelength selective polarizing filters are positioned adjacent different ones of the first and second electrodes of the liquid crystal polarization modulator.
  • the liquid crystal polarization modulator and the first and second wavelength selective polarizing filters cooperate to selectively produce the optical shutter output radiation in the visible wavelength region and the near infrared wavelength region, as determined by one of the first and second polarization states to which the filter output radiation is switched.
  • Figs. 1 A and 1 B show simulated optical transmission spectra of a first VIS/NIR optical shutter embodiment in, respectively, a visible (VIS) radiation blocking and near infrared (NIR) radiation transmitting optical shutter output state and a visible (VIS) radiation transmitting and near infrared (NIR) radiation blocking optical shutter output state.
  • VIS visible
  • NIR near infrared
  • Fig. 2 is a diagram of the optical components of the first VIS/NIR optical shutter embodiment, the optical shutter output states of which are shown in Figs. 1A and 1 B.
  • Fig. 3 is a normalized absorption curve of the wavelength selective NIR polarizer shown in Fig. 2.
  • Fig. 4 is a diagram of the optical components of a VIS/NIR shutter that includes a twisted nematic (TN) liquid crystal polarization modulator tuned to a 550 nm design wavelength.
  • TN twisted nematic
  • Fig. 5 shows simulated optical transmission spectra of the VIS/NIR shutter of Fig. 4.
  • Figs. 6A and 6B show simulated iso-contrast diagrams of the VIS/NIR shutter of Fig. 4 for, respectively, VIS radiation and NIR radiation at 805 nm.
  • Fig. 7 is a diagram of the optical components of a viewing angle- compensated version of the VIS/NIR shutter of Fig. 4.
  • Fig. 8 shows a simulated iso-contrast diagram of the viewing angle- compensated VIS/NIR shutter of Fig. 7 for NIR radiation at 805 nm.
  • Fig. 9 is a diagram of the optical components of a VIS/NIR shutter that includes a twisted nematic (TN) liquid crystal polarization modulator tuned to an 805 nm design wavelength.
  • TN twisted nematic
  • Fig. 10 shows simulated optical transmission spectra of the VIS/NIR shutter of Fig. 9.
  • Figs. 1 1 A and 1 1 B show simulated iso-contrast diagrams of the VIS/NIR shutter of Fig. 9 for, respectively, VIS radiation and NIR radiation at 805 nm.
  • Fig. 12 is a diagram of the optical components of a viewing angle- compensated version of the VIS/NIR shutter of Fig. 9.
  • Fig. 13 shows a simulated iso-contrast diagram of the viewing angle- compensated VIS/NIR shutter of Fig. 12 for VIS radiation.
  • Fig. 14 is a diagram of the optical components of a VIS/NIR shutter in which a polarization modulator includes two TN liquid crystal devices each of which is tuned to a 550 nm design wavelength.
  • Fig. 15 shows simulated optical transmission spectra of the VIS/NIR shutter of Fig. 14.
  • Figs. 16A and 16B show simulated iso-contrast diagrams of the VIS/NIR shutter of Fig. 14 for, respectively, VIS radiation and NIR radiation at 550 nm.
  • Fig. 17 is a diagram of the optical components of a viewing angle- compensated version of the VIS/NIR shutter of Fig. 14.
  • Figs. 18A and 18B show simulated iso-contrast diagrams of the VIS/NIR shutter of Fig. 17 for, respectively, VIS radiation and NIR radiation at 805 nm.
  • Fig. 19 is a diagram of the optical components of a VIS/NIR shutter in which a polarization modulator includes two TN liquid crystal devices each of which is tuned to an 805 nm design wavelength.
  • Fig. 20 shows simulated optical transmission spectra of the VIS/NIR shutter of Fig. 19.
  • Figs. 21 A and 21 B show simulated iso-contrast diagrams of the VIS/NIR shutter of Fig. 19 for, respectively, VIS radiation and NIR radiation at 805 nm.
  • Fig. 22 is a diagram of the optical components of a viewing angle- compensated version of the VIS/NIR shutter of Fig. 19.
  • Figs. 23A and 23B show simulated iso-contrast diagrams of the VIS/NIR shutter of Fig. 22 for, respectively, VIS radiation and NIR radiation at 805 nm.
  • Figs. 24A and 24B show a second VIS/NIR optical shutter embodiment, in which a guest-host effect liquid crystal polarization modulator operates with the liquid crystal director in respective first and second orientations to absorb radiation in different radiation wavelength regions and thereby alternately transmit VIS radiation and NIR radiation.
  • Figs. 25A and 25B show a third VIS/NIR optical shutter embodiment, in which a guest-host effect liquid crystal polarization modulator comprising a 270° twisted nematic liquid crystal structure operates with the liquid crystal director in, respectively, a twisted orientation to transmit VIS radiation and block NIR radiation and a vertically aligned state to transmit NIR radiation and block VIS radiation.
  • a guest-host effect liquid crystal polarization modulator comprising a 270° twisted nematic liquid crystal structure operates with the liquid crystal director in, respectively, a twisted orientation to transmit VIS radiation and block NIR radiation and a vertically aligned state to transmit NIR radiation and block VIS radiation.
  • Fig. 26 shows simulated optical transmission spectra of the VIS/NIR shutter of Figs. 25A and 25B.
  • the disclosed optical shutter is useful in a digital camera having an image sensor that operates in accordance with a time-multiplexed scheme for alternately capturing color images and depth images.
  • NIR radiation which is invisible to human eyes and transparent to conventional color filters, functions as an emitter in the performance of time-of-f light measurements that contribute to acquisition of depth data in depth image formation.
  • a 3D image sensor providing high-resolution 2D color maps and high-accuracy 3D depth maps in time-multiplexed manner is described by Seong-Jin Kim, Jungsoon Shin, James D. K. Kim, et al., "A Full-HD CMOS Image Sensor with Time-multiplexed 2D/3D Image Acquisition," 19th
  • the following disclosure describes multiple embodiments of a liquid crystal optical shutter that alternately transmits visible (VIS) radiation while blocking near infrared (NIR) radiation and then blocks VIS radiation while transmitting NIR radiation.
  • the operation of the shutter is schematically illustrated in Figs. 1A and 1 B.
  • the wavelengths of VIS radiation extend from about 380 nm to about 780 nm, and the wavelengths of NIR radiation extend from about 780 nm to about 1400 nm.
  • a first time interval shown in Fig. 1 A
  • the shutter is closed to block VIS radiation but open to transmit NIR radiation.
  • a second time interval shown in Fig. 1 B
  • the shutter is open to transmit VIS radiation but closed to block NIR radiation.
  • the disclosed liquid crystal shutter may cover only certain wavelength bands within the VIS and NIR wavelength regions rather than cover the entire VIS and NIR wavelength regions.
  • the disclosed liquid crystal shutter provides a high radiation energy throughput of the corresponding VIS and NIR wavelength bands when selected for transmission; high contrast ratio in the transmitting and blocking of radiation of respective VIS and NIR wavelength bands; rapid switching response between a first time interval when VIS radiation is blocked and NIR radiation is transmitted and a second time interval when VIS radiation is transmitted and NIR radiation is blocked; and a clear, non-scattering aperture suitable for conveying images.
  • a first VIS/NIR shutter embodiment 10 is illustrated in Fig. 2 and comprises a wavelength selective polarizer 12 for VIS and NIR radiation, also referred to as a broadband polarizer, a liquid crystal polarization modulator 14, and a wavelength selective polarizing filter pair including a wavelength selective polarizer 12 for VIS and NIR radiation, also referred to as a broadband polarizer, a liquid crystal polarization modulator 14, and a wavelength selective polarizing filter pair including a wavelength selective
  • polarizer 16 for VIS radiation and a wavelength selective polarizer 18 for NIR radiation.
  • VIS and NIR radiation is incident on broadband polarizer 12 and enters the optical component stack of VIS/NIR shutter 10 from the left.
  • the VIS and NIR radiation becomes linearly polarized in the horizontal direction after passing through broadband polarizer 12.
  • the lines shown on polarizers 12, 16, and 18 in Fig. 2 indicate the E-vector direction of the transmitted radiation.
  • the horizontally polarized radiation then passes through polarization modulator 14, which either rotates by 90° or leaves unchanged the polarization direction of the VIS and NIR radiation, depending upon the voltage applied to polarization modulator 14.
  • wavelength selective VIS polarizer 16 blocks the VIS radiation because its horizontal polarization direction is orthogonally aligned with the vertical transmission axis of wavelength selective VIS polarizer 16.
  • the remaining NIR radiation passes through wavelength selective VIS polarizer 16 and through wavelength selective NIR polarizer 18 because its horizontal polarization direction is parallel to the horizontal transmission axis of wavelength selective NIR polarizer 18.
  • wavelength selective VIS polarizer 16 passes the VIS radiation because its vertical transmission direction is now parallel to the vertical transmission axis of wavelength selective VIS polarizer 16.
  • the NIR radiation that passes through wavelength selective VIS polarizer 16 is, however, blocked by wavelength selective NIR polarizer 18 because its horizontal polarization axis is orthogonally aligned with the vertical transmission axis of the NIR radiation.
  • Wavelength selective polarizer 12 for the VIS and NIR radiation could be, for example, a wire-grid type polarizer such as the UBB01 A polarizer made by Moxtek Inc., Orem, Utah, USA or an iodine type polarizer with added dichroic dyestuff that absorbs in the NIR wavelength region or a dyestuff-type polarizer containing a series of dichroic dyes whose ranges of absorption wavelengths overlap throughout the VIS and NIR wavelength regions.
  • Wavelength selective VIS polarizer 16 could be an iodine-type polarizer, or a dichroic-type polarizer containing a mixture of red, green, and blue absorbing dyes.
  • Wavelength selective NIR polarizer 18 could contain one or more dichroic dyes that absorb radiation in the NIR wavelength region.
  • Dyestuff-type polarizing films are generally made by stretching a polymer film, such as polyvinyl alcohol, in an aqueous solution of dichroic dyes, allowing the dyed film to dry in the stretched condition, and then laminating it between two protective films of tri-acetate cellulose.
  • wavelength selective NIR polarizer 18 is approximated by an anisotropically absorbing film having a Gaussian absorption lineshape peaking at 805 nm with a full width at half height of 80 nm and a dichroic ratio of 100.
  • a normalized absorption curve of this film is illustrated in Fig. 3.
  • the dichroic ratio of a film at a particular wavelength is the ratio of the
  • wavelength selective VIS polarizer 16 is assumed to be an ideal polarizer for wavelengths up to 700 nm, beyond which there is no absorption
  • broadband VIS/NIR polarizer 12 is assumed to be an ideal polarizer for wavelengths up to 1000 nm.
  • Polarization modulator 14 selectively does not rotate or rotates by 90° the polarization direction of incident light, depending upon the applied voltage. Suitable candidates for liquid crystal polarization modulators for the disclosed liquid crystal shutter implementations include an ECB type liquid crystal device with a
  • homogeneously aligned liquid crystal material having a positive dielectric anisotropy a VAN type liquid crystal device with a homeotropically aligned liquid crystal material having a negative dielectric anisotropy, a pi-cell liquid crystal device, a ferroelectric liquid crystal device, and a twisted nematic (TN) liquid crystal device.
  • Fig. 4 is a diagram of the optical components of a VIS/NIR shutter 10-i, in which the polarization modulator is a right-handed 90° TN device ⁇ 4 ⁇ that operates in the so-called first minimum mode at a design wavelength of 550 nm, where the human eye is most sensitive.
  • the birefringence, ⁇ , of the liquid crystal material and the cell gap, d, of TN device ⁇ 4 ⁇ are chosen to satisfy the first minimum criteria:
  • An-d/A 1 ⁇ 2 3 , where ⁇ is the design wavelength.
  • a liquid crystal material with a birefringence of 0.225 requires a 2.12 ⁇ -cell gap to satisfy the first minimum condition at 550 nm.
  • the polarization direction of radiation propagating through the output side of TN device 14i when no voltage is applied is linearly polarized and is perpendicular to the linear polarization direction of radiation propagating through the input side of TN device 14-
  • VIS/NIR shutter 10i tuned for 550 nm are shown in Fig. 5.
  • a controller 30 applies a 0 V signal 32 to set TN device 14i to its OFF state
  • TN device 14i rotates by 90° the 90°-input polarization direction of radiation incident on TN device 14 ⁇ i at 550 nm so that light polarized at 0° exits TN device 14-
  • This 0° polarization direction is perpendicular to the 90° transmission axis of wavelength selective VIS polarizer 16, and the transmittance is essentially zero at the design wavelength of 550 nm.
  • VIS light visible radiation
  • elliptically polarized light exits TN device 14 ⁇ , so that a certain amount of VIS light leaks through wavelength selective VIS polarizer 16.
  • This light leakage results in an overall transmitted luminance of 0.444%, taking into account the spectral response of the human eye.
  • the light is also elliptically polarized so that a certain amount of NIR radiation is absorbed by wavelength selective NIR polarizer 18.
  • the transmittance at 805 nm is 39.1 %.
  • the transmission curve for the case of TN device 14i in its OFF state at 0 V is shown by the solid curve in Fig. 5.
  • controller 30 applies a 12 V signal 32 to set TN device ⁇ 4 ⁇ to its ON state
  • TN device 14i imparts no rotation of the polarization direction of radiation incident on TN device 14 ⁇ i so that radiation remaining linearly polarized at 90° exits TN device 14-
  • This 90° polarization direction is parallel to the 90° transmission axis of wavelength selective VIS polarizer 16, and the VIS light passes through it without absorption. The result is a 50% transmitted luminance and a contrast ratio of 1 12.6 over the visible spectrum.
  • the light In the NIR wavelength region of the spectrum, the light is also linearly polarized at 90°, but this polarization direction is perpendicular to the 0° transmission axis of wavelength selective NIR polarizer 18, leading to maximum absorption and NIR radiation transmittance at 805 nm of 0.338%, and thereby resulting in a contrast ratio of 1 15.6 at 805 nm.
  • the transmission curve for the case of TN device 14 ⁇ i in its ON state at 12.0 V is shown by the dotted curve in Fig. 5.
  • TN device 14i in its normally black (NB) mode between parallel aligned polarizers, which is known to have a wide range of high-contrast viewing angles.
  • NB normally black
  • the viewing angles in the NIR wavelength region of the spectrum Fig. 6B
  • TN device 14i operates in its normally white mode (NW) between perpendicularly aligned polarizers, which is known to have narrow range of high-contrast viewing angles.
  • NW normally white mode
  • TN device 14 ⁇ i has the optical properties akin to those of a positive C film.
  • Fig. 7 shows a VIS/NIR shutter 10i C , which differs from VIS/NIR shutter 10- 1 , in that a negative C retarder film 40i is positioned between wavelength selective VIS polarizer 16 and wavelength selective NIR polarizer 18 for viewing angle compensation.
  • the placement of negative C retarder film 40i allows it to improve the viewing angles in the NIR wavelength region without affecting the already wide viewing angles in the VIS wavelength region.
  • FIG. 8 shows an iso-contrast diagram in the NIR wavelength region at 805 nm for the case in which negative C retarder film 40-I has a retardation of 300 nm.
  • a comparison of Fig. 8 with Fig. 6B shows that negative C retarder film 40i markedly improves the range of high-contrast viewing angles at 805 nm.
  • the iso-contrast diagram for VIS light is unaffected by negative C retarder film 40i .
  • Fig. 9 is a diagram of the optical components of a VIS/NIR shutter I O 2 , in which the cell gap and birefringence of a TN device 14 2 are tuned for the first minimum condition at a design wavelength of 805 nm in the NIR wavelength region.
  • Wavelength selective VIS polarizer 16 and NIR polarizer 18 are rotated by 90° from their polarization axis orientations of VIS/NIR shutter I O- 1 of Fig. 4.
  • a first minimum at 805 nm corresponds to a 3.10 ⁇ -cell gap for a liquid crystal material with a birefringence of 0.225.
  • Fig. 10 The transmission spectra of VIS/NIR shutter 10 2 tuned for 805 nm are shown in Fig. 10.
  • controller 30 applies a 0 V signal 32 to set TN device 14 2 to its OFF state
  • TN device 14 2 rotates 90° the 90°-input polarization direction of radiation incident on TN device 14 2 at 805 nm so that radiation polarized at 0° exits TN device 14 2 .
  • This 0° polarization direction is perpendicular to the 90° transmission axis of wavelength selective NIR polarizer 18, and the transmittance is 0.339% at the design wavelength of 805 nm.
  • elliptically polarized light exits TN device 14 2 , so that a certain amount of VIS light is absorbed by wavelength selective VIS polarizer 16, reducing the transmitted luminance to 44.9%.
  • the transmission curve for the case of TN device 14 2 in its OFF state at 0 V is shown by the solid curve in Fig. 10.
  • controller 30 applies a 12 V signal 32 to set TN device 14 2 to its ON state
  • TN device 14 2 imparts no rotation of the polarization direction of radiation incident on TN device 14 2 so that radiation remaining linearly polarized at 90° exits TN device 14 2 .
  • This 90° polarization direction is perpendicular to the 0° transmission axis of wavelength selective VIS polarizer 16, and the VIS light is totally extinguished for all VIS wavelengths.
  • This VIS light extinction results in a theoretically infinite contrast ratio over the visible spectrum.
  • the light In the NIR wavelength region of the spectrum, the light is also linearly polarized at 90°, but this polarization direction is parallel to the 90° transmission axis of wavelength selective NIR polarizer 18, leading to minimum absorption and NIR radiation transmittance at 805 nm of 47.4%, and thereby resulting in a contrast ratio of 139.8.
  • the transmission curve for the case of TN device 14 2 in its ON state at 12 V is shown by the dotted curve in Fig. 10.
  • wavelength regions can be readily compared.
  • FIG. 9 The dependence of contrast ratio on the angle of incident light on VIS/NIR shutter 10 2 Of Fig. 9 is illustrated by the iso-contrast diagrams for VIS light in Fig. 1 1A and for NIR radiation at 805 nm in Fig. 1 1 B.
  • the viewing angles for high-contrast viewing in the NIR wavelength region are relatively wide because for this case the dark state is determined by TN device 14 2 in its normally black (NB) mode between parallel aligned polarizers.
  • NB normally black
  • TN device 14 2 operates in the normally white mode (NW) in which the dark state acts as a positive C retarder film.
  • NW normally white mode
  • the viewing angles for a NW TN device can be improved with an external negative C retarder film or a WV compensator film.
  • Fig. 12 shows a VIS/NIR shutter 10 2 c, which differs from VIS/NIR shutter I O2 in that negative C retarder film 40 2 is positioned between wavelength selective NIR polarizer 18 and wavelength selective VIS polarizer 16 for viewing angle compensation.
  • Fig. 12 shows that the locations of wavelength selective VIS polarizer 16 and NIR polarizer 18 are interchanged, but not the orientations of their polarization axes.
  • the placement of negative C retarder film 40 2 allows it to improve the viewing angles in the VIS wavelength region without affecting the already wide viewing angles of the NIR wavelength region.
  • Fig. 13 shows an iso-contrast diagram in the VIS wavelength region for the case in which negative C retarder film 40 2 has a retardation of 500 nm.
  • FIG. 13 A comparison of Fig. 13 with Fig. 1 1A shows that negative C retarder film 40 2 markedly improves the range of high-contrast viewing angles in the VIS wavelength region.
  • the iso-contrast diagram for NIR radiation is unaffected by negative C retarder film 40 2 .
  • Fig. 14 is a diagram of the optical components of a VIS/NIR shutter I O3, in which a polarization modulator 14 3 comprises two TN devices 14 3A and 14 3B .
  • First TN device 14 3A has a right-handed 90° twist
  • second TN device 14 3B has a left- handed 90° twist.
  • TN devices 14 3A and 14 3B are placed together such that the surface alignment rubbing directions at the radiation input surfaces of TN devices 14 3A and 14 3B are parallel to each other.
  • the birefringence, ⁇ , of the liquid crystal material and the cell gap, d, of TN devices 14 3A and 14 3B are chosen such that they operate in the first minimum mode at a design wavelength of 550 nm.
  • the transmission axes of broadband polarizer 12 and wavelength selective VIS polarizer 16 are parallel to each other. There is no absorption of VIS light and maximum absorption of NIR radiation because the transmission axes of broadband polarizer 12 and wavelength selective NIR polarizer 18 are perpendicular to each other.
  • the transmission curve for this case is shown by the solid curve in Fig. 15. For unpolarized incident light, the transmittance is 50% over the visible spectrum, and the transmittance at 805 nm is 0.336%.
  • the transmission curve for this case is shown by the dotted curve in Fig. 15.
  • the VIS light transmission is zero at 550 nm, the wavelength in which the first minimum condition is precisely met, but then increases for wavelengths of VIS light somewhat above and below 550 nm.
  • the result is an overall transmitted luminance of 0.402% with a transmittance of 39.1 % in the NIR wavelength region at 805 nm.
  • the luminous contrast in the VIS wavelength region is 124.4, and the contrast at 805 nm is 1 16.3.
  • the contrast ratio is the ratio of the transmitted luminance in the visible region of the light exiting VIS/NIR shutter I O3 during the first subframe (bright state) divided by the transmitted luminance exiting VIS/NIR shutter 10 3 during the second subframe (dark state). Because the contrast ratio is primarily determined by the dark state when first TN device 14 3A is in its ON state, modulator 14 3 has some optical characteristics of a positive C retarder film. In Fig. 16B, the contrast ratio is the ratio of the ratio of the
  • modulator 14 3 has optical characteristics similar to those of a negative C retarder film. This makes it difficult to simultaneously widen the range of high-contrast viewing angles in both the VIS and NIR wavelength regions because modulator 14 3 has opposite optical characteristics in these two regions.
  • adding an external negative C retarder film would improve the viewing angles through compensation in the VIS wavelength region in which modulator 14 3 exhibits positive C character, but would worsen the viewing angle angular behavior in the NIR wavelength region in which modulator 14 3 already exhibits negative C character.
  • VIS wavelength selective polarizer 16 and wavelength selective NIR polarizer 18 are separate films that control non-overlapping parts of the electromagnetic spectrum, it is possible to independently change the angular properties of modulator 14 3 in the separate spectral regions by providing different retarder film compensators or combinations of retarder film compensators in front of a first wavelength selective polarizer and between a first wavelength selective polarizer and a second wavelength selective polarizer.
  • a VIS/NIR shutter 10 3C shown in Fig. 17 is an example of an optical shutter in which such a viewing angle compensation technique is applied to modulator 14 3 .
  • VIS/NIR shutter 14 3C constitutes a modification of VIS/NIR shutter 10 3 of Fig.
  • a negative C retarder film 40 3 at the entrance side of polarization modulator 14 3 (between broadband polarizer 12 and first TN device 14 3A ) and a positive C retarder film 50 3 between wavelength selective VIS polarizer 16 and wavelength selective NIR polarizer 18.
  • the value of negative C retarder film 40 3 is chosen to optimize the viewing angle in the VIS wavelength region. This optimum is unaffected by the value of positive C retarder film 50 3 because it is located downstream of wavelength selective VIS polarizer 16.
  • the value of positive C retarder film 50 3 is chosen to optimize the viewing angle in the NIR wavelength region.
  • Negative C retarder film 40 3 also affects the viewing angle in the NIR wavelength region, so this is the reason why the viewing angle in the VIS wavelength region is first optimized. Simulations indicate that a 300 nm negative C retarder film 40 3 and a 450 nm positive C retarder film 50 3 simultaneously optimize the viewing angles in both the VIS and NIR wavelength regions. Figs. 18A and 18B show the remarkable improvement in viewing angles compared with those of viewing angle uncompensated cases of Figs. 16A and 16B.
  • a general rule can be stated for independently optimizing the angular properties an optical shutter operating in two non-overlapping wavelength regions.
  • a first optical retarder in the optical series is optimized for a first wavelength region in a first step; and then a second optical retarder in the optical series is optimized for a second, non-overlapping wavelength region in a second step.
  • the first optical retarder is located in front of a first wavelength selective polarizer covering a first wavelength region, and the second optical retarder is located between the first wavelength selective polarizer and a downstream positioned second wavelength selective polarizer covering a second, non-overlapping wavelength region.
  • Fig. 19 is a diagram of the optical components of a VIS/NIR shutter 10 4 , in which a polarization modular 14 4 comprises two TN devices 14 4A and 14 4B.
  • VIS/NIR shutter 10 differs from VIS/NIR shutter 10 2 in the following two respects.
  • polarization modulator 14 a cell gap of 3.10 ⁇ is chosen to shift the first minimum condition to 805 nm, the peak absorption wavelength of wavelength selective NIR polarizer 18.
  • Wavelength selective VIS polarizer 16 and wavelength selective NIR polarizer 18 have been rotated by 90° from the polarization axis orientation shown for VIS/NIR shutter IO 3 in Fig. 14.
  • the transmission axes of broadband polarizer 12 and wavelength selective VIS polarizer 16 are perpendicular to each other.
  • There is total extinction of VIS light and maximum transmittance of NIR radiation because the transmission axes of broadband polarizer 12 and wavelength selective NIR polarizer 18 are parallel to each other.
  • the transmission curve for this case is shown by the dotted curve in Fig. 20.
  • the transmittance is 0% over the visible spectrum, and the transmittance at 805 nm is 47.4%.
  • the light exiting polarization modulator 14 3 is no longer linearly polarized light rotated by 90°, but rather is elliptically polarized light that becomes partly absorbed by wavelength selective VIS polarizer 16, reducing the transmitted luminance to 44.9%.
  • the luminous contrast in the VIS wavelength region is, therefore, theoretically infinite, and the contrast at 805 nm is 140.9.
  • the range of viewing angles in the VIS wavelength region of the spectrum and the NIR wavelength region of the spectrum can be independently optimized by providing optical retarder films at strategic locations in the optical path of VIS/NIR shutter 10 4 .
  • a VIS/NIR shutter 10 4C shown in Fig. 22 is an example of an optical shutter in which the range of viewing angles is optimized.
  • the range of viewing angles is optimized in the VIS wavelength region in a first step by introducing a 100 nm negative C retarder film 40 at the entrance of polarization modulator 14 4 (between broadband polarizer 12 and first TN device 14 A ), and the range of viewing angles in the NIR wavelength region of the spectrum is optimized in a second step by introducing a 350 nm +C retarder film 50 4 between wavelength selective VIS polarizer 16 and wavelength selective NIR polarizer 18.
  • the resulting iso-contrast diagrams are shown for VIS light in Fig. 23A and for NIR radiation at 805 nm in Fig. 23B. Comparison of the diagrams of Figs. 23A and 23B with the uncompensated iso-contrast diagrams of Figs 21 A and 21 B reveals that the range of high-contrast viewing angles is enlarged, especially in the NIR wavelength region.
  • VIS/NIR shutter 60 operates using the guest-host effect, in which dichroic dye guest molecules are dissolved in a liquid crystal host mixture and orient themselves with their long axes along the director of the host liquid crystal material. Dichroic dyes absorb radiation anisotropically and thereby cause the guest-host mixture to exhibit variable absorption depending upon the orientation of the liquid crystal director relative to the direction of the electric field vector of incident linearly polarized radiation.
  • guest-host systems There are two different types of guest-host systems: positive guest-host systems, which show maximum absorption for incident radiation polarized along the liquid crystal director and minimum absorption for radiation polarized perpendicular to the liquid crystal director; and negative guest-host systems, which show minimum absorption for incident radiation polarized along the liquid crystal director and maximum absorption for radiation polarized perpendicular to the liquid crystal director.
  • Positive guest-host systems comprise positive dichroic dyes, in which the transition moment of the dye generally lies in a direction parallel to the long axis of the dye molecule.
  • Negative guest-host systems comprise negative dichroic dyes, in which the transition moment of the dye generally lies in a direction perpendicular to the long axis of the dye molecule.
  • a guest-host system can be both positive and negative when the host mixture comprises both positive and negative dyes.
  • Figs. 24A and 24B are diagrams of, respectively, a negative dye absorbing and positive dye non-absorbing state and a negative dye non-absorbing and positive dye absorbing state of guest-host system 60 comprising broadband linear polarizer 12 and a liquid crystal cell or device 62 fabricated with both positive and negative dyes.
  • the director n of the host liquid crystal material is oriented in a direction perpendicular to cell electrodes 66, and 66 e .
  • This perpendicular orientation would be the case either for a vertically aligned nematic (VAN) device having homeotropic alignment and a liquid crystal host characterized by negative dielectric anisotropy and receiving zero applied voltage or below threshold applied voltage or, alternatively, for a homogeneously aligned liquid crystal device having a liquid crystal host characterized by positive dielectric anisotropy and receiving an applied voltage several times above threshold voltage.
  • VAN vertically aligned nematic
  • the positive dyes are indicated in Fig. 24A by elongated cigar-shaped molecules, with their long axes oriented in a direction parallel to the liquid crystal director n.
  • broadband polarizer 12 for the VIS/NIR region is placed at the radiation input side of guest-host system 60.
  • the input polarized radiation in a first absorption wavelength band characteristic of the positive dye is therefore weakly absorbed.
  • the negative dyes are indicated in Fig. 24A by disk- shaped molecules, with their normal axes also parallel the liquid crystal director n.
  • the input polarized radiation in a second absorption wavelength band characteristic of the negative dye is therefore strongly absorbed.
  • Fig. 24B the director of the host liquid crystal material has been rotated by 90°, but remains in the plane of the drawing.
  • the 90° rotation of the liquid crystal director would correspond to the case in which a voltage that is several times the threshold voltage is applied to the electrodes.
  • the 90° rotation of the liquid crystal director would correspond to the case in which either a zero voltage or a voltage below the threshold voltage is applied.
  • light in the first wavelength band, characteristic of the positive dye is strongly absorbed
  • light in the second wavelength band characteristic of the negative dye
  • the positive dye could be a single dye or dye mixture having a first absorption
  • the negative dye could be a single dye or a mixture of three or more negative dyes having a second absorption wavelength band covering the entire VIS wavelength region of the spectrum, as described, for example, by V. Chigrinov, et. al in the Japanese Journal of Applied Physics, Part 1 , Volume 42, Number 3, pages 1297-1300 (2003).
  • the positive dye mixture could have an absorption wavelength band covering the entire VIS wavelength region
  • the negative dye could be a negative dye or dye mixture covering part or all of the NIR wavelength region.
  • a third VIS/NIR shutter embodiment 70 is illustrated in Figs. 25A and 25B.
  • a liquid crystal cell 72 of VIS/NIR shutter 70 is a guest-host device comprising a 270° twisted nematic liquid crystal structure, similar to that of an STN device, which has dissolved, positive dichroic dye molecules that absorb radiation in the NIR
  • Liquid crystal cell 72 is positioned between an input polarizer 74, and an exit polarizer 74 e that each linearly polarize radiation in the VIS wavelength region of the spectrum but have no effect in the NIR wavelength region of the spectrum.
  • the transmission axes of polarizers 74, and 74 e are orthogonally aligned. In Fig. 25A, the transmission axes of polarizers 74, and 74 e are set at 90° angles relative to the alignment directions on the adjacent input surface of an electrode 76, and the adjacent output surface of an electrode 76 e of 270° twisted nematic liquid crystal cell 72. This results in the so-called o-mode of operation in visible light, which gives a wide viewing angle.
  • VIS/NIR shutter 70 operates as follows. With respect to operation in the VIS wavelength region of the electromagnetic spectrum, at zero applied voltage, the nematic director, indicated by the fine straight lines in Fig. 25A, twists 270° along a straight line path from one of electrodes 76, and 76 e to the other.
  • the 270° twisted nematic liquid crystal structure acts as a 270° linear polarization rotator would act if its cell gap, d, satisfies the following equation where ⁇ is the design wavelength, typically 550 nm, and ⁇ is the birefringence of the nematic liquid crystal mixture.
  • the nematic liquid crystal material has no effect on the polarization state of visible radiation passing through it, and linearly polarized visible light propagating from input polarizer 74, is blocked by polarizer 74 e , resulting in 0% visible light transmission.
  • the operation of 270° twisted nematic cell 72 in the visible spectrum is very similar to that of a conventional 90° twisted nematic cell.
  • the dark cigar-shaped molecules in Fig. 25A represent dissolved positive, dichroic NIR wavelength absorbing dye molecules whose long axes follow the 270° twisted structure. Skilled persons will recognize that the optical eigenmodes in such a 270° twisted structure can be quite elliptically polarized or nearly circularly polarized. This phenomenon is described at length by T. Scheffer and J. Nehring in a chapter devoted to guest-host displays in The Physics and Chemistry of Liquid Crystal Devices, G. Sprokel Ed., Plenum Press, N.Y., pages 173-198 (1979).
  • the radiation entering liquid crystal cell 72 is unpolarized and can be considered to be resolved into two orthogonal, elliptically unpolarized eigenmodes that both are strongly absorbed by the dissolved NIR dye. This results in low transmittance for zero applied voltage.
  • the nematic structure may be approximated by a vertically aligned nematic director structure as shown in Fig. 25B, in which the positive, dichroic NIR absorbing dyes are vertically oriented along with the liquid crystal director. In this orientation, the transition moment of the dye is perpendicular to the E-field of the incoming unpolarized NIR radiation and very little absorption occurs, resulting in high radiation transmission.
  • the nematic liquid crystal material used in the simulation was the nematic mixture MLC-7030 available from Merck, Darmstadt, Germany.
  • the wavelength dispersion of the birefringence of MLC-7030 was included in the simulations.
  • the birefringence at the design wavelength of 550 nm was 0.1 126.
  • the cell gap was chosen according to equation [1 ] to be 6.46 ⁇ .
  • the simulations assumed a broadband NIR absorber 12 having a constant extraordinary absorption coefficient of 0.09 nm "1 and a constant ordinary absorption coefficient of 0.009 nm "1 , for a dichroic ratio of 10. For wavelengths shorter than 780 nm, the visible range, both the ordinary and extraordinary absorption coefficients were set to zero.
  • Fig. 26 shows a simulation of the transmission spectrum of this device for the two switched states.
  • the transmission of radiation achieves a maximum of 50% at the 550 nm design wavelength.
  • the transmission of radiation drops close to zero, resulting in a contrast ratio in the thousands.
  • the transmission of radiation is about 35% at 850 nm, and at zero volts the transmission of radiation drops to around 3.5% at 850 nm, with a resulting contrast ratio of around 10.
  • Polarizers 74, and 74 e could be of the NIR absorbing type referred to in the first embodiment of this disclosure, and the VIS absorbing positive dichroic dye could be a mixture of dichroic dyes with overlapping absorption bands in the VIS region of the type referred to in the second embodiment of this disclosure.

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Abstract

La présente invention concerne un obturateur optique (10) qui comprend un filtre polarisant à sélection de longueur d'onde (12) en association optique avec un modulateur de polarisation à cristaux liquides (14) afin de commuter rapidement entre des états optiques pour transmettre de façon alternée un rayonnement visible et un rayonnement proche infrarouge. Le filtre polarisant à sélection de longueur d'onde est conçu pour conférer un état de polarisation à un rayonnement incident et transmettre un rayonnement polarisé dans au moins la région de longueur d'onde visible du spectre électromagnétique. Le modulateur de polarisation à cristaux liquides est positionné pour recevoir un rayonnement incident pour la propagation interne à travers le modulateur de polarisation à cristaux liquides et est sensible à une première valeur et à une seconde valeur d'un signal de commande appliqué (32) pour commuter le rayonnement se propageant en interne vers, respectivement, un premier état de polarisation et un second état de polarisation. La commutation entre les premier et second états de polarisation produit, en coopération avec le filtre polarisant à sélection de longueur d'onde, un rayonnement de sortie de l'obturateur optique dans différentes régions de longueur d'onde du spectre électromagnétique.
PCT/US2013/022287 2012-01-19 2013-01-18 Obturateur optique à commutation rapide permettant de transmettre de façon alternée un rayonnement visible et un rayonnement proche infrarouge WO2013109979A1 (fr)

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